Hello, I just bought this tandem on Craigslist. It is a late 60's or early 70's model. It is stuck in5 th gear. It will shift down to 1 st by moving the shifter lever but as soon as you let go it shifts right back into 5 th. gear. Any advice on how to adjust it would be greatly appreciated, thanks, Huck L Berry

To fix this, tighten the wing nuts on the sides of the "Twin Stik" shifter. This will increase the friction so the shifter will hold against the force of the derailleur spring. You can see the wing nuts on the left and right side in the following picture:

If the wing nuts are fairly tight and still slip, you may have to take it apart and clean everything. Just unscew the wing nut and clean all the grease and dirt off the washers. Do one side at a time in case you mix up what order the washers go back in. Reassemble without any lubricant.